The AIMS of the study are 1) to determine the safety, tolerance, clinical and endoscopic response, immunogenicity, and pharmacokinetics of a single dose of 5, 10 and 20 mg/kg cA2, as compared to a single dose of placebo, in a double-blind, randomized study in patients with active Crohn's disease and 2) to evaluate the safety, tolerance, clinical response and immunogenicity of subsequent repeated treatment with 10mg/kg of cA2 compared with placebo, in a double blind, randomized study in patients with Crohn's Disease.